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 METALLURGICAL
Weathering Steel, J. J. Cecilio
CASE ML1 -
Problem:
Failure of weathering steel ASTM A-690, A-588 and A-242.
Reoccurring cycle of rusting and flaking off under failure of the
Symptoms:
section.
Collection of Facts: The copper bearing low alloy steels defined above
CORRODE RAPIDLY IF NOT BOLDLY EXPOSED TO THE ELEMENTS OF SUN, RAIN AND WIND.
These steels are marketed under ASTM A-690, A-588 and A-242. Their trade
names are Corten, Marten and Mariner. To prevent buildup of salt or other
contaminants during the wetting and drying cycle, any portions of a structure
not boldly exposed to the elements must be protected by painting or by the
application of a barrier.
Solution: Structural elements made of weathering steel that may build up
salts and other contaminants shall be painted with a transparent varnish.
Further information can be obtained from U.S. Steel Company.
ASTM-A-609 Mariner steel piling, wetting and drying portions should be blasted
clean to near white metal and then coated by a 40 mil-carboglass 1601
polyester glass flake. Source is the Carboline Company.
Use of Special Materials - Antennas, E. L. Mifflin
CASE ML2 -
Problem:
Selection of special high strength material.
Contractors declined to bid on project.
Symptom:
Collection of Facts: A design for a tall tower utilized 90,000 psi heat
treated alloy steel in order to reduce the size and weight of members. The
material required special welding specifications and resulted in a structure
which contractors declined to bid on. There were only three well qualified
potential bidders and all initially declined to bid. Two bidders flatly
refused to consider undertaking the project. The third bidder finally agreed
to a negotiated contract. The use of the material selected increased the cost
by an estimated 2.5 million dollars and the total cost was undoubtedly
increased because it was not possible to obtain competitive bids. Needless to
say, the negotiated price was not favorable to the government.
Solution: Investigate all aspects of cost and availability before using
special materials. Material that requires welding should be avoided for tower
construction.
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